Electrostatic precipitator and a collecting electrode therefor



Nov. 5, 1957 N. F. SOHLMAN ETAL 2,812,035

ELECTROSTATIC PRECIPITATOR AND A COLLECTING ELECTRODE THEREFOR Filed Sept. 9, 1555 3 Sheets-Sheet 1 35 f I //WE/VTO/?5 /\///5 F 50/7/0700 PRIOR ART 9 Hugh Mu//e/7 F/ G. 7 Henry Cflahrmann By their af/omeys Nov. 5, 1957 N. F. SOHLMAN ETAL 2,812,035

ELECTROSTATIC PRECIPITATOR AND A COLLECTING ELECTRODE THEREFOR Filed Sept. 9, 1955 3 Sheets-Sheet 2 Hug/7 Mal/A90 Henry Cflohrmonn By #7617 affomeys ELECTROSTATIC PRECIPITATOR AND A COLLECTING ELECTRODE THEREFOR Filed Sept. 9, 1955 N. F. SOHLMAN ETAL Nov. 5, 1957 I5 Sheets-Sheet 3 WVfA/TORS /\//'/5 F. Sch/man 36 Hug/7 Mullen Henry C. Dob/mam By their altar/lays United tates Patent '0 M Application September 9, 1955, senal'No. 533,429

4 lairns. (Cl.

This inventionreles toi an electrostatic precipitatinfor removing 'dust pa icles from a gas stream, and more paiticularly to a collectin t, such a precipitator. lnthe dry type pre th' oust particles'are remo d om th g s, tr am semi-can ha theniwith ele trons and era mg them to, ground-escall' t n e es. i tidathe tim ame strength of th elec rost tic fiel one of themes; ana ram p ob lems in desigii a'rid operatioii offdr'yty'pe precipitators is the removal of the collected material from the collecting electrodes without redispersing it in the gas stream. The St el tting electrodes by rapping at frequent intervals, thus caiisin'g the material to be dislodged, and collecting Qiie Qof the common types of collecting electrodes in dry precipitators is one which is shaped in the fornl of -a m'etalli'c plate. Such plates are arranged a iii l ne with one another, forming a wall or panel en each two rows of the wires Which constitute the t'tiflg file'et r'od'es. There are several alternate rows of emit the electrode wires and collecting plate electrodes. It is the object of this invention'to provide an improved form ofplate collecting electrode and a precipitator contaming it.

. in the drawings:

N Fig. l i's a perspective view of a collecting electrode rel 'an 'ele'ctrical precipitator made in accordance with pi eseiit invention, with the trailing edge of the panel tr wn-a thel'ett.

2 i s a view in horizontal cross section of the collectin'g electrode of Fig. 1, taken on the line 2-2 of i i c is a face elevation of the same collecting electrode.

is 'a view in elevation of the interior of an electrical precip'tator made in accordance with the invention, the 'view being t'aken in a plane parallel to a wall or panel of co lecting elements, with the outer wall of the precipitator removed. c I Fig. 5 is 'a perspective view of the main portion of a precipitate} made in accordance with the invention, parts being broken away to show more clearly the collecting el od s and the rapping mechanism for them.

Fig. 15 isa perspective view of half a dozen of the of the rapping mechanism for the collecting eieejt'r'eaesor Figs. 4 and 5.

Fig. 7 is an edge view of a collecting electrode of the pricrart. t v

Successfulprecipitation depends largely on the design of the coll ect in-g electrodes. They must not buckle or because that would reduce the electrical clearance and'p revent operation of the precipitatoryat maximum vo age. The most common way of ensuring that plate collecting electrodesmaintain their distances and yet are adequately shaken when rapped, is to have the electrodes opp'ositeeach other in the successive rows of Walls bolted together by bars running transversely through the "machine and then s'imultaneouslyrapping all of the electrodes ardtnictho'd of doing this is to jar the collecting and r 2,812,035 Patented Nov. 5, 1957 attached to any one rod. These rods serve as spacers to' preserve the electrical distances. It is convenient, of course, to have them at the middle of the electrodes, i. e. intermediate the length of the electrodes, that being the point at which the greatest movement will occur.

The're is a great disadvantage in this construction. When collecting electrodes are rapped there is a tendency for a puff of smoke to be ejected from the precipitator. In machines of the common type above described, the electrodes are about three feet in width and the number of rods required to connect them is few. In such machines, about one-fourth of the electrodes are rapped simultaneously, and therefore puffs of smoke oeeur. According to aplicants invention it is possible to avoid these puffs of smoke. The present machineraps only about one-thirtieth of the total number of electrodes in the precipitator at any one rap. This, of course, avoids y P n It has also been found that there are limits to the length of electrodes which can maintain their rigidity during vibration of rapping. Since rigidity longitudinally of the electrodes is needed in order to maintain the electrical distances, it has been found desirable to have the edges formed to give stiffness wherever possible. Bends of various kinds have-heretofore been made at the longitudinal edges, not only to give stiiiness but also to assist in collecting any dust knocked loosefrom the electrodes. However, the electrodes heretofore knownwere not entirely satisfactory. Some were'made by a bending PIGS? ess but the modulus of the sections thus obtained was not very satisfactory. A common shape is shown in Fig. 7. It has been found impossible by such bending processes to evolve a battle 8 in one piece which would help to catch dust particles on both sides of the electrode." Here tofore an extra member was riveted or welded onto the plate to assist in obtaining this catching on both sides The prior art hook 9 is also not as rigid as desired. It has been found impossible to keep the plate straight and rigid when any elements are welded to it in this manner. The precipitator illustrated inFigs. l to 6 of the drawings has the usual shell with a top wall 39-, side wall 37 and end walls 38. Underneath are two dust collecting hoppers 40. In one end wall 38 there is a gas inlet 10 forthe gas which is to be cleaned, and in the other end Wall is agas outletll. for the clean gas (see Fig. 5).

' Inside the inlet 10 are gas distribution bafli'es 1-2 (see 17 on top of the shell.

Like many other precipitators, this precipitator consists of parallel gas passages formed by walls of flat collecting plate electrodes. In the center of each such gas passage are mounted emitting electrodes 13. These elec trodes are shown in the form of wires. The collecting electrodes are vertical plates 14 such as shown in Figs. 1,2 and 3.

As already mentioned, to ensure maximum voltage within the effective volume of an electric precipi-tator, positive positioning and accurate spacing between the col:- lecting and emitting electrode systems are essential under operational stress. Rigidity longitudinally, i. e. vertically, is needed in the collecting electrodes in order to main tain the electrical distance between the collecting and emitting electrodes. There is another requirement which must be filled by a collecting electrode; It will be noted that the gas stream is flowing horizontally by on both sides of each wall. When an electrode is rapped, the tendency is for the loosened particles to be carried elong'past the neighboring electrode. This 'must be prevented. The trailing edge of a collecting electrode therefore is made to provide some form of hook to catch the particles and make them drop down into the hoppers 40 without being carried past the next electrode. Such a hook may be described as a batfie. The prior art electrode of Fig. 7 has many disadvantages, the principal one being the fact that the welding tends to distort the plate and it is virtually impossible to straighten it again without resorting to some sort of pressing or rolling pressure which, of course, adds to the cost considerably. Furthermore, the weld is also subject to failure by fatigue, since these plates are vibrated repeatedly by the rapping mechanism. It has therefore been necessary to use rivets to prevent the added plate from falling off the electrode proper and shorting .out the precipitator in the event that the'weld fails. These electrodes were made by a process which was not capable of making tubular cross sections.

We have found that it isdesirable to make the collecting electrode by a continuous die-drawing method. This electrode is shown in Figs. 1, 2 and 3. It is made by running a strip of steel through a series of consecutive rolls, each of which forms the plate a little bit more than the preceding one, so that as the plate comes from the last roll it is formed with the shape in cross section which is desired of the final. article and the article is entirely a one-piece construction. By this method of fabrication, a straight electrode is produced with no weld at the edge. Heretofore in order to get electrodes of sufficient length, two pieces were welded together end to end. These welds were uneven in thickness, which was a bad feature electrically and gave the electrodes a tendency to split when they were turned to shape.

The right-hand or leading edge of the electrode of the present invention is in the form of a tube 15 running throughout the longitudinal length of the electrode. This tubular right edge gives the maximum stiffness because it has the best section modulus around an axis in the plane of the plate. The trailing edge of the electrode, i. e. the left edge as the electrode appears in Figs. 1 and 3, must provide the baflle as well as stiffness. It has been found that by a continuous drawing process a good section modulus can be obtained by what may be called three-fourths of a complete tube. It will be seen that the edge is formed by first rolling it to one side and then folding back and making a corresponding rolled edge on the other side, giving in effect a folded-back, curled umbrella or mushroom shape in cross section. This gives the necessary gutter like or baffle on each side, with a double strength or rigidity on one side and a total section modulus about three-fourths of that of a complete circle. This edge is designated in the drawings by the reference character 16. In order to suspend the electrode a hook 34 is provided which can be welded to the top of the electrode proper. At the bottom there is provided a tab 35 with a pin 36 projecting laterally therefrom to provide proper connection with the rapping mechanism. The tube or pipe edge 15 is preferably about one inch in diameter and the other edge 16 curled back on itself has approximately the same maximum diameter.

The rapping mechanism for the collecting electrodes is driven by a small motor 18 at the base of the shell (see Fig. This drives a sprocket 19 by means of a roller chain 20, as shown in Fig. 4. This sprocket is tight on a hammer shaft 21. running transversely of the shell of the precipitator.. The hammer shaft has a multiplicity of small rappers 22 fixedly mounted on it at different circumferential positions (see Fig. 5). As can be seen from Figs. 5 and 6, each of these rappers 22 has a link 23 at fixed circumferential positions around the shaft and freely hinged thereon is an arm 24 carrying a hammer roll 25. There is a rapper 22 for each wall of electrodes in the machine, and below each such rapper is a shock bar 26. The hammer roll 25 is adaptedto be flung against the end of the shock bar by steady rotation of the hammer shaft 21, as can be seen most clearly perhaps in Figs. 4 and 6.

In Fig. 4 it will be noticed that each bottom tab 35 of an electrode lies in a slot 27 in its shock bar 26 and is limited in its position longitudinally of the shock bar by collars 28. These collars permit a slight movement of the shock bar relative to the electrodes. The result is that a blow by the hammer roll on the shock bar 26 gives a sharp knock to each electrode laterally in the plane of the panel or wall. In order to prevent the shock bar from being displaced permanently and to return it to its operative position for the next blow, a stop bar 41 is provided on each shock bar. The resilience of the electrodes with the combination of these stop bars 41 returns the shock bar to its initial position after the blow has been transmitted and received.

The rapping mechanism for the emitting electrodes is unchanged by the present invention and raps the electrodes at their midpoints. It consists of a channel iron 29 run ning from the inlet side to the outlet side of the precipitator on each line of emitting electrodes 13, and a transverse ,angle iron 30 connecting those channel irons. Hammers 31 pivotally mounted as shown in Fig. 4 are adapted to transmit blows to the channel irons which, being fastened to the midpoints of the emitting electrodes 13, shake them. The hammers 31 are given a swinging movement to produce these blows by means of a cam 32 on a rotatable shaft 33 driven by mechanism (not shown) at the top of the precipitator.

What is claimed is:

1. A collecting electrode for an electrostatic precipitator comprising a metallic electrode having two vertical longitudinal edges integral therewith to stiffen the electrode, one edge being tubular in cross section and the other edge being formed of metal extending first to one face of the electrode and then doubled back to the other face thus forming semi-circular bafiles on both faces of the electrode facing toward the opposite edge of the electrode adapted to hold dust particles travelling with the gas flow; whereby the electrode has a rigidity modulus of section at the second edge higher than that due to a plain baflle of the same arcuate shape.

2. In an electrostatic precipitator for removing suspended dust particles from a gas stream, a housing through which the gas stream passes horizontally, and emitting electrodes arranged vertically in parallel rows whose planes lie in the direction of movement of the gas, in combination with walls parallel thereto each composed of collecting electrodes, each electrode having the trailing vertical edge formed integrally with the rest of the electrode and folded first to one face of the electrode and then doubled back to the other face to form semicircular bafiles on both faces of the electrode facing opposite to the gas stream, and the other vertical edge having a tubular form; and rapping means adapted to transmit raps to the ends of the collecting electrodes.

3. A collecting electrode for an electrostatic precipitator comprising a unitary metallic plate and longitudinal edges integral therewith, one longitudinal edge being formed of the metal of the electrode and folded first to one face and then to the other of the electrode to form semi-circular baffles on both faces of the electrode adapted to hold dust particles travelling with the gas flow and to strengthen the plate against bending, in combination with a second longitudinal edge rolled into tubular form; whereby each longitudinal edge of the electrode has a high rigidity modulus of section to stiffen the electrode.

4. In an electrostatic precipitator for removing sus pended dust particles from a gas stream, a housing through which the gas stream passes horizontally, parallel spaced rows of emitting electrodes, the planes of the rows lying in the direction of movement of the gas, and collecting electrode walls parallel to and intercalated with the emitting electrode rows consisting of flat electrodes attached to the precipitator at the top and bottom ends, each electrode having its trailing longitudinal vertical edge shaped in cross section like a semi-circle to form battles on both faces of the flat electrode to catch particles near it travelling with the gas stream, said trailing edge being integral with the rest of the flat electrode and folded so as to be two-ply on at least one face of the electrode and the leading edge being tubular in cross section; in combination with a shock bar below each collecting electrode wall and attached to the lower ends of the electrodes in that wall, and individual rapping means for each shock bar; whereby each shock bar can be rapped separately and yet the electrodes maintain their spacing.

6 References Cited in the file of this patent UNITED STATES PATENTS 1,854,650 Gies Apr. 19, 1932 2,595,204 Richardson Apr. 29, 1952 FOREIGN PATENTS 471,795 Germany Feb. 21, 1929 646,736 France July 17, 1928 

